The issue is girls congregating the streets for three hours and not going to a particular place
The key question is where are they congregating? In front of a beis medrish or a place where men constantly go and come?
yb613, if that’s the case then you have a justified complaint. So to find out if your complaint is justified I would speak to other bucharim and see what they have to say about this inyan. If there is indeed a problem with girls congretating in places where they shouldn’t be, then discuss this with a Rosh Yeshiva and if they find that there is indeed a problem that justifies a solution, they can call the girls principles from school and work out a solution such as girls cannot congregate on a particlur block where men constantly go and come.
If it’s girls congregating in one particular area let’s say in front of someone’s house and that house is not located near a shul then the girls cannot be asked not to congregate there. If you find it disturbing perhaps you can find a different route to where you need to go to circumvent passing the girls.